RU2458922C2 - Method of producing 4,4-dimethyl-1,3-dioxane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to petrochemical industry and more precisely to production of monomers for synthesis of polymers. More specifically, the invention relates to methods of producing 4,4-dimethyl-1,3-dioxane (DMD) which is used as an intermediate product in production of isoprene and polyisoprene rubber. The method is realised via condensation of isobutylene, taken in form of an isobutylene-containing fraction, with formaldehyde in form of an aqueous solution in the presence of an acid catalyst at temperature 75-105°C, pressure 1.5-2.5 MPa in a column reactor, while feeding reactant streams through direct flow from bottom-up into the reactor, separating the reaction mass into water and oil layers, evaporating the water layer, adding the starting aqueous formaldehyde solution to the residue after evaporation and recirculation of the obtained mixture into the condensation zone, with separation of the end product and high-boiling by-products from the oil layer via fractionation. Condensation is carried out in a reactor consisting of separate, series-connected 2-6 sections lying one on top of the other, with successive combined feeding of reactant streams down each section through a nozzle of a distribution device, outlet of the reaction mass from the top of each section, cooling in an external heat exchanger and feeding down the next section.

EFFECT: method reduces the amount of by-products to 190-200 kg per 1 ton of DMD, increases DMD output by 2,5-4% from the same amount of reactants and reduces the amount of metal used to make the reactor by about three-fold.

Description

The invention relates to the petrochemical industry, more specifically to the field of monomers for the synthesis of polymers. More specifically, the invention relates to methods for producing 4,4-dimethyl-1,3-dioxane (DMD), which is used as an intermediate in the production of isoprene and polyisoprene rubber.

A known method of producing DMD by condensation of isobutylene in the form of an isobutylene-containing fraction C ₄ with formaldehyde in the form of an aqueous solution in the presence of sulfuric acid as a catalyst at a temperature of 85-95 ° C, a pressure of 1.8-2.0 MPa. The synthesis of DMD is carried out in columnar tubular reactors, which are a system of pipes enclosed in a common casing. The coolant (water) is fed into the annulus of the reactor. An acidic aqueous solution of formaldehyde and an isobutylene-containing fraction C ₄ are supplied countercurrently to the tube space of the reactor, the fraction being supplied to the lower part of the tube space through a distributor with nozzles located inside each pipe. In the upper and lower parts of the reactor are settling zones. In the upper settling zone, the reaction mass is divided into water and oil layers. DMD and high boiling point by-products (WFP) are isolated from the oil layer by distillation. The aqueous layer containing sulfuric acid and the runway is neutralized with alkali, then evaporated. The residue after evaporation, containing salts and runways, is sent to the wastewater of the production [Ogorodnikov S.K. and Idlis G.S. Isoprene production. - L .: Chemistry, 1973, p. 48-58]. The disadvantages of this method are the presence of wastewater contaminated with salts and runways, a significant amount of runways - production waste.

Closest to the claimed is a known method for producing DMD by condensation of isobutylene in the form of an isobutylene-containing fraction C ₄ with formaldehyde in the form of an aqueous solution in the presence of oxalic acid at a temperature of 80-100 ° C, a pressure of 1.6-2.0 MPa using column tubular reactors. An acidic aqueous solution of formaldehyde and an isobutylene-containing fraction C ₄ are fed directly into the lower part of the tube space of the reactor, and the fraction is fed through a distribution device. The coolant (cooled steam condensate) is fed into the annulus. From the upper settling zone of the reactor, the reaction mass is fed in two separate streams to the lower part of the next reactor. The reaction mass, taken from above the last reactor, is divided into oil and water layers. The aqueous layer was evaporated, the initial formaldehyde aqueous solution was added to the residue after evaporation, and the resulting mixture was recycled to the condensation zone. DMD and runway are isolated from the oil layer by rectification [Kirpichnikov P.A., Beresnev V.V., Popova L.M. The album of technological schemes of the main industries of the synthetic rubber industry. - L .: Chemistry, 1986, p.41-46, prototype].

In this method, the reaction water layer is recycled, all reaction products are removed only with the oil layer, and the content of the products in the water layer is stabilized at a certain level.

The disadvantage of this method is the formation of a significant amount of runway - waste that is not used in the process itself (the amount of runway is 225-230 kg per 1 ton of DMD obtained). Another drawback is the far from complete and not rational use of the volume of reactors used for the synthesis of DMD and the resulting high costs of metal - stainless steel for their manufacture.

In the known method, the interaction of isobutylene with formaldehyde occurs mainly in the tube space of the reactor, where small drops of isobutylene-containing fraction C ₄ float. In settling zones, the target reaction occurs to a small extent, since there the reaction mass exfoliates and the interfacial contact surface of the reactants sharply decreases. At the same time, in sedimentary zones in an acidic water layer with the participation of formaldehyde, DMD undergoes side conversions with the formation of a runway. The fraction of settling zones in such a reactor is quite large and amounts to approximately half of the total reaction volume, and the volume of the annulus (non-reaction) space is approximately equal to the volume of the reaction space. In addition, in such a reactor, isobutylene-containing droplets formed as a result of dispersion through nozzles that are immiscible with water and, when floating up in long pipes (15 m high), gradually stick together and coarsen, which leads to a decrease in the contact interface of the reactants and, accordingly, to a decrease in the rate and selectivity of the DMD formation reaction.

The objective of the proposed method is to reduce the amount of waste from the process of producing DMD, increase the efficiency of using the volume of reactors for the synthesis of DMD and reduce the cost of metal for their manufacture.

This problem is solved by the method of producing DMD by condensation of isobutylene in the form of an isobutylene-containing C ₄ fraction with formaldehyde in the form of an aqueous solution in the presence of an acid catalyst at elevated temperature and pressure, by supplying streams of the initial reagents from the bottom up to the column type reactor (vertical cylindrical apparatus), by separating the reaction mass on the water and oil layers, by evaporation of the aqueous layer, adding to the residue after evaporation of the initial aqueous solution of formaldehyde and recirculation of the resulting mixture into the condensation zone, with separation by distillation from the oil layer of DMD and runway. The process is carried out in a reactor consisting of separate 2-6 sections arranged one above the other in series. Reagent flows are fed together to the bottom of each section through the nozzles of the switchgear, the reaction mass is discharged on top of each section, cooled in an external heat exchanger and fed to the bottom of the next section.

The process is carried out using one or more series and / or parallel connected sectionalized reactors.

Oxalic acid, phosphoric acid, or a mixture of these acids is used as the acid catalyst.

Condensation is carried out at a temperature of 75-105 ° C, a pressure of 1.5-2.5 MPa.

The difference of the proposed method from the prototype is that the condensation is carried out in a reactor consisting of separate, located one above the other, connected in series 2-6 sections.

Another difference is that the reagent flows are fed together to the bottom of each section through the nozzles of the switchgear.

Another difference is that the reaction mass is removed from the top of each section, cooled in an external heat exchanger and fed to the bottom of the next section.

The joint supply of reagent flows through the nozzles of the distribution device can improve the dispersion of the isobutylene-containing fraction of C ₄ in the reactor and to obtain smaller drops. There are no settling zones in the reactor; therefore, the contacting of the reagents occurs in the entire reaction volume. Repeated dispersion of the isobutylene-containing fraction C ₄ in each of 2-6 sections allows avoiding the negative effect of sticking and coarsening of the pop-up drops. By reducing the number of sections in the reactor to 1 (while maintaining the reaction volume), the effect of adhesion and coarsening of the pop-up drops is manifested. With an increase in the number of sections over 6, this effect is not manifested, however, the metal consumption for the manufacture of the reactor increases. Intermediate cooling of the reaction mass between sections in an external heat exchanger ensures that the set temperature in the reactor is maintained and excess heat is removed without using the reactor volume.

The proposed method allows to reduce the number of runways to 190-200 kg per 1 ton of DMD, increase the production of DMD by 2.5-4% of the same amount of reagents and reduce the amount of metal for the manufacture of the reactor by about three times.

Industrial application of the proposed method is illustrated by examples.

Example 1

The DMD synthesis process is carried out using a reactor consisting of four separate metal sections made of 10Kh17N13M2T steel in series with each other. Each reaction section is a vertical pipe insulated on both sides with an inner diameter of 200 mm and a height of 3750 mm. Sections are located one above the other and combined into a single vertical apparatus.

The upper part of the 1st, 2nd and 3rd sections (the numbering of sections starts from the bottom of the reactor) is connected to the corresponding 1st, 2nd and 3rd external heat exchanger, each of which is also connected to the lower part of the next section , respectively, 2nd, 3rd and 4th. Water is supplied to the heat exchangers as a heat carrier. At the bottom of each section is a switchgear in the form of a tube bundle with nozzles. The total reaction volume of this apparatus is 450 liters.

In the lower part of the 1st section of the above-described reactor serves isobutane-isobutylene fraction with an isobutylene content of 43.4% of the mass. at a rate of 140.0 kg / h, as well as a formaldehyde mixture, which is an aqueous solution containing 31.2% of the mass. formaldehyde, 1.7% of the mass. oxalic acid and 1.3% of the mass. phosphoric acid at a rate of 180.0 kg / h. The streams of the starting reagents are fed to the section together through the nozzles of the switchgear.

The reaction mass is removed from the upper part of the 1st section, cooled in a heat exchanger, and then fed to the lower part of the 2nd section. From the upper part of the 2nd section, the reaction mass is withdrawn, cooled in a heat exchanger, fed to the lower part of the 3rd section, and then similarly sent through the heat exchanger to the 4th section.

In the reactor, the temperature is 92-97 ° C, the pressure is 1.9-2.0 MPa.

Leaving from the upper part of the 4th section, the reaction mass is divided into water and oil layers.

The aqueous layer was evaporated, the residue after evaporation was mixed with the initial aqueous solution of formaldehyde, then the resulting mixture was recycled to the reactor as a formaldehyde charge.

The oil layer is washed with water, then subjected to distillation processing to isolate the products of the synthesis of DMD.

At the first (along the flow of the oil layer) distillation column, the spent isobutane-isobutylene fraction with an isobutylene content of 12.0% by weight is distilled off, which is sent to the isobutane dehydrogenation process.

The bottom liquid of the first column is fed to the second distillation column, where the trimethylcarbinol fraction is distilled off, which is recycled to the reactor.

The bottom liquid of the second column is fed to the third distillation column, where DMD is distilled off in an amount of 71.0 kg / h. The residue after distillation of DMD in the amount of 13.4 kg / h is a runway. The number of runways per 1 ton of DMD obtained is 189 kg.

The conversion of formaldehyde is 80.1%, the conversion of isobutylene is 82.2%.

DMD is sent to the isoprene production process, which is then used to produce polyisoprene rubber. Runways are disposed of by known methods.

Example 2

The process is carried out analogously to example 1, however, there are the following differences.

The synthesis of DMD is carried out in a reactor consisting of six isolated sections. Each section has an internal diameter of 200 mm and a height of 2500 mm. The sections are connected in series with five outdoor heat exchangers.

The concentration of isobutylene in the spent isobutane-isobutylene fraction is 11.7% of the mass.

The production of DMD is 71.7 kg / h, the production of runways - 13.5 kg / h. The number of runways per 1 ton of DMD obtained is 188 kg.

The conversion of formaldehyde is 80.8%, the conversion of isobutylene is 82.7%.

Example 3

The process is carried out analogously to example 1, however, there are the following differences.

The synthesis of DMD is carried out in a reactor consisting of three isolated sections. Each section has an internal diameter of 200 mm and a height of 5000 mm. The sections are connected in series with two external heat exchangers.

The concentration of isobutylene in the spent isobutane-isobutylene fraction is 12.5% of the mass.

The production of DMD is 69.7 kg / h, the production of runways - 13.7 kg / h. The number of runways per 1 ton of DMD obtained is 197 kg.

The conversion of formaldehyde is 79.2%, the conversion of isobutylene is 81.3%.

Example 4

The process is carried out analogously to example 1, however, there are the following differences.

The synthesis of DMD is carried out in a reactor consisting of two isolated sections. Each section has an inner diameter of 200 mm and a height of 7500 mm. The sections are connected in series with one external heat exchanger.

The concentration of isobutylene in the spent isobutane-isobutylene fraction is 13.5%.

The production of DMD is 68.1 kg / h, the production of runways - 13.7 kg / h. The number of runways per 1 ton of DMD obtained is 201 kg.

The conversion of formaldehyde is 77.8%, the conversion of isobutylene is 79.7%.

Claims (3)

1. The method of producing 4,4-dimethyl-1,3-dioxane by condensation of isobutylene in the form of an isobutylene-containing fraction C ₄ with formaldehyde in the form of an aqueous solution in the presence of an acid catalyst at elevated temperature and pressure, carried out in a column type reactor, with direct flow of reactants from bottom to top in the reactor, separation of the reaction mixture into water and oil layers, evaporation of the aqueous layer, addition of formaldehyde to the residue after evaporation of the initial aqueous solution, and recirculation of the resulting mixture into the condensation zone, with division by distillation from the oil layer of the target product and high-boiling by-products, characterized in that the condensation is carried out in a reactor consisting of separate, one above the other, connected in series 2-6 sections, with sequential joint supply of reagent flows to the bottom of each section through the distribution nozzles devices, with the conclusion of the reaction mass on top of each section, cooling in an external heat exchanger and feeding the next section to the bottom. 2. The method according to claim 1, characterized in that oxalic acid, phosphoric acid or a mixture of these acids is used as the acid catalyst. 3. The method according to claim 1, characterized in that the condensation is carried out at a temperature of 75-105 ° C, a pressure of 1.5-2.5 MPa.